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<a href="00865.html" target="topic">第十二章 随机约束</a>, <a href="00930.html" target="topic">主题</a></div>
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12.11 范围变量的随机化 — std::randomize()</div>
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内建的类随机化方法对类成员变量执行专有的操作。使用类来对需要随机化的数据建模是一种强大的机制，它使得我们能够产生通用、可复用的包含随机变量的对象，并能够产生可以在以后扩展、继承、约束、过载、使能、关闭、以及从其它对象合并或分离的约束。类及与其关联的随机变量和约束在处理上的方便性使得类非常适合描述和处理随机数据和约束。然而，某些要求较少的问题并不需要类的这些完整的灵活性，它可以使用一个较为简单的机制来随机化不属于一个类的数据。范围随机函数（<span style="color: #0000FF">std</span><span style="color: #800080">::</span><span style="color: #0000FF">randomize</span><span style="color: #800080">()</span>）使得用户能够随机化当前范围内的数据，而无需定义一个类或实例化一个类对象。 </p>
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范围随机化函数的语法如下： </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00453"><pre class="Element12">scope_randomize ::= // 没有包含在附录A中
[<strong><span style="color: #FF0000">std::</span></strong>]<strong><span style="color: #FF0000">randomize(</span></strong>[variable_identifier_list]<strong><span style="color: #FF0000">)</span></strong> [<strong><span style="color: #FF0000">with</span></strong> constraint_block]</pre></div></div>
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<strong>语法12-10 — 范围随机化函数语法（没有包含在附录A中）</strong></p><p class="Element10">
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范围随机化函数与类的随机化方法的作用相同，只是它操作于当前范围内的变量而不是类成员变量。函数的参数指定了那些需要赋值为随机值的变量，也就是随机变量。 </p>
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例如： </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00454"><pre class="Element12"><span style="color: #0000FF">module</span> stim<span style="color: #800080">;</span>
<span style="color: #0000FF">bit</span> <span style="color: #800080">[</span><span style="color: #FF0000">15</span><span style="color: #800080">:</span><span style="color: #FF0000">0</span><span style="color: #800080">]</span> addr<span style="color: #800080">;</span>
<span style="color: #0000FF">bit</span> <span style="color: #800080">[</span><span style="color: #FF0000">31</span><span style="color: #800080">:</span><span style="color: #FF0000">0</span><span style="color: #800080">]</span> data<span style="color: #800080">;</span>
<span style="color: #0000FF">function bit</span> gen_stim<span style="color: #800080">();</span>
<span style="color: #0000FF">bit</span> success<span style="color: #800080">,</span> rd_wr<span style="color: #800080">;</span>
success <span style="color: #800080">=</span> <span style="color: #0000FF">randomize</span><span style="color: #800080">(</span>addr<span style="color: #800080">,</span> data<span style="color: #800080">,</span> rd_wr<span style="color: #800080">);</span> <span style="color: #008000">// 调用std::randomize</span>
<span style="color: #0000FF">return</span> rd_wr<span style="color: #800080">;</span>
<span style="color: #0000FF">endfunction</span>
...
<span style="color: #0000FF">endmodule</span></pre></div></div>
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函数<span class="Element146">gen_stim</span>调用<span style="color: #0000FF">std</span><span style="color: #800080">::</span><span style="color: #0000FF">randomize</span><span style="color: #800080">()</span>函数并带有三个变量作为参数：<span class="Element146">addr</span>、<span class="Element146">data</span>、和<span class="Element146">rd_wr<span style="color: #0000FF"></span>std</span><span style="color: #800080">::</span><span style="color: #0000FF">randomize</span><span style="color: #800080">()</span>将新的随机变量赋值到那些在<span class="Element146">gen_stim</span>函数范围内可见的变量。注意，<span class="Element146">addr</span>和<span class="Element146">data</span>具有模块级的作用范围，而<span class="Element146">rd_wr</span>具有函数内的本地作用范围。我们也可以使用类来编写上面的例子： </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00455"><pre class="Element12"><span style="color: #0000FF">class</span> stimc<span style="color: #800080">;</span>
<span style="color: #0000FF">rand bit</span> <span style="color: #800080">[</span><span style="color: #FF0000">15</span><span style="color: #800080">:</span><span style="color: #FF0000">0</span><span style="color: #800080">]</span> addr<span style="color: #800080">;</span>
<span style="color: #0000FF">rand bit</span> <span style="color: #800080">[</span><span style="color: #FF0000">31</span><span style="color: #800080">:</span><span style="color: #FF0000">0</span><span style="color: #800080">]</span> data<span style="color: #800080">;</span>
<span style="color: #0000FF">rand bit</span> rd_wr<span style="color: #800080">;</span>
<span style="color: #0000FF">endclass</span>
<span style="color: #0000FF">function bit</span> gen_stim<span style="color: #800080">(</span>stimc p<span style="color: #800080">);</span>
<span style="color: #0000FF">bit</span> success<span style="color: #800080">;</span>
success <span style="color: #800080">=</span> p<span style="color: #800080">.</span><span style="color: #0000FF">randomize</span><span style="color: #800080">();</span>
addr <span style="color: #800080">=</span> p<span style="color: #800080">.</span>addr<span style="color: #800080">;</span>
data <span style="color: #800080">=</span> p<span style="color: #800080">.</span>data<span style="color: #800080">;</span>
<span style="color: #0000FF">return</span> p<span style="color: #800080">.</span>rd_wr<span style="color: #800080">;</span>
<span style="color: #0000FF">endfunction</span></pre></div></div>
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然而，对于这个简单的应用，范围随机化函数能够产生一个更直接的实现。 </p>
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如果范围随机化函数成功地为所有的随机变量设置了有效值，那么它返回1；否则它返回0。如果调用范围随机化函数的时候没有指定参数，那么它作为一个检查器使用，并简单地返回状态。</p></div>
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<a href="00042.html" target="topic">12.11.1 为范围变量添加约束 — std::randomize() with</a> </div></td><td class="Element206" valign="top" width="50%">
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范围随机化函数的<span style="color: #0000FF">std</span><span style="color: #800080">::</span><span style="color: #0000FF">randomize</span><span style="color: #800080">() </span><span style="color: #0000FF">with</span>形式允许用户为本地范围变量指定随机约束。当说明约束的时候，范围随机化函数的参数指定的变量变成了随机变量，所有其它变量被认为是状态变量。 </div></td></tr></table></div></div>
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